The present invention refers to the field of semiconductor memories and, in particular, to a selector or column multiplexer for semiconductor memories.
As is known, for semiconductor memories the selection of a generic cell in the reading stage takes place by selecting the row to which the cell belongs to bring it to a selected potential and the column of the specific cell to connect it to a reading circuit. The reading circuit can, for example, perform current type reading of the cell. Selection of the column takes place via a suitable column multiplexer. In general, the column multiplexer comprises two input lines for supplying the two reading signals which, in the case of current reading, are composed of a sensing voltage and a ground voltage.
Furthermore, the multiplexer is provided with selective connection means necessary to select two specific column lines or bit lines among a plurality of column lines of the memory matrix to connect the two input lines to the two specific column lines. In conventional column multiplexers, transistors made, for example in MOSFET technology, are used to select the two specific column lines. The transistors have the gate terminal connected to a respective control line which has a level signal such as to activate or deactivate the transistor. The signal present on each control line is obtained by decoding an address signal.
It has been noted that, for particular applications, the functional characteristics and the architecture of conventional column multiplexers may not be satisfactory regarding both the complexity of managing the selection operations and concerning the overall dimensions when they are integrated into semiconductor structures. For example, it has been observed that, while for memories which adopt a so-called xe2x80x9cNORxe2x80x9d, or xe2x80x9cdouble Txe2x80x9d, traditional structure, implementation of current reading of the memory cells using conventional multiplexers can be convenient, on the contrary for contactless and virtual ground memories, the limits of conventional multiplexers appear more significant.
An object of the present invention is to provide a column multiplexer having additional functions compared to those known in the art so that it can be used efficiently for particular operational requirements.
The object of the present invention is achieved by a column multiplexer for a memory matrix having memory cells arranged in rows and columns. The multiplexer includes input lines for input signals, a plurality of output lines for electrical connection to the columns of the matrix, a selective connection device for selecting, in a first operation mode, at least one output line of the plurality of output lines in such a way as to connect it selectively to the input lines. In the first operation mode, the selective connection device selects a first group of output lines among the plurality of output lines, including at least three first lines.